1. Field of the Invention
The present invention relates to a method of manufacturing an electroluminescence display device capable of displaying a predetermined number of characters, more particularly to improvements in the method of manufacturing a Chip-On-Glass-type EL display device, in which bare integrated circuit, chips not packed in plastics, are directly attached on a glass plate.
2. Discussion of Related Art
In a known EL display device shown in FIG. 1, there is provided a display panel, capable of displaying a predetermined number of characters, which is attached on a glass plate. Integrated circuit packages 3 in which integrated elements used for driving the display panel are packed in plastics are attached to a film or printed circuit board 2. Thereafter, the electrodes of the integrated circuit packages 3 and the display panel 1, are connected to each other by wires 4.
In this known EL display device using the conventional integrated circuit package 3, since a film or a printed circuit board 2 is used as a medium for the connection of the integrated circuit package 3 to the display control circuit (not shown), production cost is increased, and it is cumbersome to make such an EL display device. Further, it is difficult to miniaturize and lighten the EL display device because of the use of the integrated circuit package 3 packed in plastics therein.
In another type of EL display device, as shown in FIGS. 2 and 3, a bare chip 12, not packed in plastics is directly attached on glass plate 11. This is usually called the COG type (Chip-On-Glass type).
In detail, there is provided a soda glass plate 11 on which a protective lqyer 13 is laid. The protective layer 13, a SiO.sub.2 layer, is produced by evaporation and has a thickness of about 1500.ANG.. This layer 13 serves to prevent diffusion of Alkali properties of the soda glass plate 11 such as Na and K. On the protective layer 13 is formed a lower electrode 14 which is produced by means of sputtering and photoetching of ITO (Indium Tin Oxide). Thereon, a lower insulating layer 15 of either Y.sub.2 O.sub.3 or Si.sub.3 N.sub.4, a fluorescent layer 16 of ZnS : Mn, and an upper insulating layer 17 of either Y.sub.2 O.sub.3 or Si.sub.3 N.sub.4 are in turn laid by sputtering. Each of such layers has a thickness of about 3000.ANG., 5000.ANG.and 3000.ANG.respectively.
On the upper insulating layer 17 are laid upper electrodes 18 which are produced by means of evaporation and photoetching of Al. Layers 18 have a thickness of about 1500.ANG.. At the side of the electrode 14 and on the protective layer 13 is formed a panel lead 19 produced by evaporating Ni spaced from the bare chip 12. Thereafter, a back glass plate of thin film 20 produced by means of photoetching is attached to the soda glass plate 11, and has an exhaust port 20'. A vacuumized space 21 is provided for moisture proofing the insulating layers 15, 17 and the fluorescent layer 16. The space 21 is to be filled with moisture proof insulating oils such as silicon oil or grease through the port 20'. The display novel 23 is completed by sealing the port 20' with sealing material 22.
Further, the unpacked bare chip 12 for driving the display panel is fastened to the end portion of the soda glass plate 11 by use of an adhesive 24 such as epoxy resin or silver-glass paste. The Al electrode 12' of the bare chip 12 and the panel lead 19 are connected to each other by ultrasonic bonding of Al or Au wire 25. The Al or Au wire has a diameter of about 25-30 .mu.m. To protect the bare chip 12 from exterior influences, it is covered with a package 26 made of ceramic or non-metallic material and sealed with special epoxy resin 27. Between the back glass plate 20 and the package 26 is formed a wire support member 28 of glass material produced by means of evaporation or screen printing, whereby the mechanical strength of the Al or Au wire is further increased. The bare chip 12 is connected to display control circuitry through an external lead 29.
This prior COG type EL display device, however, proved in practice to be ineffective and somewhat impractical since it requires the protective layer 13 of SiO.sub.2 to protect the bare chip 12 which may be damaged as a result of contact of the soda glass plate 11 with moisture in the atmosphere, followed by the dissociation of Al property from the glass plate 11 and the action of the dissociated Al property upon Al electrode 12 of the bare chip 12.
Further, it has disadvantages that the bare chip 12 may not be fastened rigidly and firmly to the soda glass plate 11 because of the use of the adhesive 24 without the use of special apparatus, that the different heights between the Al electrode 12' of the bare chip 12 and the panel lead 19 make the ultrasonic bonding of Al or Au wire 25 difficult, that the special package 26 is needed to the bare chip 12 from external influences, and that the special wire support member of glass material 28 is needed for increasing the mechanical strength of the Al or Au wire.